Motivated by our interest in the relation of permeability and energetic factors to the active transport of sodium, we are attempting to develop non-invasive optical techniques to measure transmembrane potentials and reduction levels of metabolic intermediates in the toad bladder. We are searching for dyes which show fluorescence or absorbance changes dependent on changes in the transepithelial potential. (Other groups have found dyes which respond to potential changes in simpler systems.) We are also studying the response of NADH fluorescence to manipulation of metabolic conditions. The one earlier study of this nature was hampered by the severe light scattering problem in toad bladder. Modification of a novel dual-wavelength spectrometer we have developed allows a correction for light scatter in fluorescence studies. BIBLIOGRAPHIC REFERENCES: Ogan, K., Beach, K.W., Caplan, S.R., and Essig, A., A multiple-wavelength spectrometer. Biophysics J. 16:63a, 1976. Cecchi, X., Canessa, M., Essig, A., and Edelman, I.S., Phosphorylation of 2-deoxyglucose in toad bladder as an index of cytoplasmic ATP/ADP ratios. Fed. Proc. 35:703, l976.